The present invention relates generally to hydraulically actuated pumping element assemblies, and more particularly to the hydraulic biasing of pumping elements in hydraulically actuated devices, such as fuel injectors.
In one class of fuel injectors, fuel is pressurized to injection levels by a hydraulically driven pumping element. In a typical example, the pumping element includes a relatively large diameter intensifier piston that is acted upon by actuation fluid pressure, such as high pressure lubricating oil, and a relatively small diameter plunger that has one end in contact with fuel in a pressurization chamber. In a typical fuel injection system of this type, a common rail supplies pressurized actuation fluid to a plurality of fuel injectors. Each injector includes a control valve that is opened to initiate an injection event by supplying high pressure actuation fluid to the top side of the intensifier piston. When the control valve is open, high pressure actuation fluid acts on the intensifier piston and drives both it and the plunger downward to pressurize the fuel for the injection event. Between injection events, the plunger and piston are retracted and reset for a subsequent injection event. This retracting is typically accomplished by an appropriate positioning of a compressed return spring or, in some instances, by channeling pressurized fluid to the underside of the intensifier piston.
In order to retract the plunger/piston assembly between injection events using a spring, there is usually a need to add additional parts in order to couple these two components so both retract in unison. One way of accomplishing this is to machine an annular groove on the outer surface of the plunger and couple the plunger to the piston using a ring in contact with a retainer clip that is received in the groove of the plunger.
In the case where pressurized actuation fluid is applied to the underside of the piston to cause the pumping element to retract, some means must be provided for attaching the plunger to the piston. One strategy in this regard is to machine the plunger and piston from a single component. However, this is often undesirable because both the piston portion and the plunger portion must be guided to relatively tight tolerances in different guide bores.
Still another alternative method to retracting the pumping element between injection events is to maintain the fuel at a sufficient pressure that fuel pressure alone refilling the pressurization chamber is sufficient to cause the pumping element to retract. However, this strategy must necessarily require the fuel to be maintained and plumbed around an engine at relatively higher pressures than desirable, and the retraction sequence necessarily requires extensive valving strategies that permit the necessary pressure differentials to cause the pumping element to retract. In all of these retracting strategies, additional components are needed, and assembly problems must be overcome, in order to successfully incorporate one of these retraction strategies into a fuel injector.
Engineers are constantly seeking ways to reduce part count and to improve the ability for an injector to be easily assembled for mass production. The present invention is directed to overcoming these and other problems associated with decreasing part count, increasing injector robustness, and improving the ability of an injector to be easily assembled.
A hydraulically biased pumping element assembly includes a body that defines an unobstructed biasing passage that is substantially fluidly isolated from a pumping chamber. A pumping element is positioned in the body and is moveable between a retracted position and an advanced position. The pumping element has a biasing surface exposed to fluid pressure in the unobstructed biasing passage, and a pressurization surface exposed to fluid pressure in the pumping chamber.